Radar systems and other communication systems using high frequency signals, such as in the gigahertz range, typically require a sophisticated antenna system that has a very high coverage, including 360.degree. azimuth coverage and a high range in elevation. Some antenna systems provide a 360.degree. azimuth coverage and a high elevation range without having to mechanically move the antenna. Other antenna systems require complicated motors and gears for moving an antenna mast. These antennas may include a plurality of antenna elements positioned on an antenna face, forming an antenna array. Some antenna arrays were mechanically steered, with a power splitter driven by a single amplifier, or a multi-panel phased array having a transmit/receive module positioned behind each antenna element. Some of these systems also required complex controllers or were physically large, and thus, not mobile.
U.S. Pat. No. 5,243,354 to Stern, et al., U.S. Pat. No. 5,543,811 to Chethik, and U.S. Pat. No. 5,552,798 to Dietrich, et al. all disclose multi-panel antennas for allowing 360.degree. azimuth coverage. In the '798 Dietrich patent, antenna elements are supported by various panels of an antenna mast. The antenna panels enable a spread spectrum communication between terminals over a range of elevation angles. However, the system requires a centralized radio frequency power source.
U.S. Pat. No. 5,146,230 to Hules discloses a radar array using only transmit/receive modules to make it possible to generate a radio frequency signal directly at an antenna element and set the relative phase relationships between the elements. The transmit/receive modules also pre-amplify a receive signal. These transmit/receive modules avoid those problems related to a totally centralized radio frequency power source. For example, those antenna feed systems using a centralized radio frequency power source usually have constrained feed or space feed power distribution systems. Typically, these centralized systems also have dividers and combiners that could introduce undesirable inter-element interference and losses.
In the '230 patent to Hules, these drawbacks of using centralized feed systems are overcome by the use of active transmit/receive modules that generate the radio frequency power directly at the antenna elements. Thus, the relative phase relationship between the elements can be established. Additionally, individual transmit/receive modules allow preamplification of the received signal within an amplifier that is part of the transmit/receive module. However, in many systems, the transmit/receive modules were placed at each antenna element, adding to the production costs, the weight of the overall unit, and efficiency of the design.
The antenna system disclosed in the '230 patent to Hules overcomes this problem by using a switching mechanism that controls the connection of each transmit/receive module to a passive antenna element. Thus, each transmit/receive module is connected to only one antenna element at a time. The switches are controlled so that the active transmit/receive module is connected to desired patterns of passive antenna elements that are circularly arranged in an annular layered configuration. The antenna elements and active transmit/receive modules are positioned along the outer portions of respective antenna layers, with various antenna connecting leaves located in anterior portions of the layers. The switch is operable to connect the active transmit/receive modules with successive patterns of mutually adjacent antenna elements to produce antenna beams with desired directionality and phase relationships.
However, the antenna structure disclosed in the '230 patent to Hules discloses an annular configuration that has only a circular antenna face, and a constant circular arrangement of antenna elements that are organized into three 120.degree. sectors, A, B and C, of four passive antenna elements each. Although a 360.degree. azimuth is covered, the surface of the various sectors forming an antenna face are perpendicular to the ground, and do not appear to provide adequate elevation range. Additionally, the antenna elements are arranged along a 120.degree. sector forming part of the annular face. Thus, none of the different antenna elements forming an array are disposed in one plane, which would aid in beam forming.